title: Relationship between sublethal injury and microbial inactivation by the combination of high hydrostatic pressure and citral or tert-butyl hydroquinone.
abstract: The aim was to investigate (i) the occurrence of sublethal injury in Listeria monocytogenes, Escherichia coli, and Saccharomyces cerevisiae after high hydrostatic pressure (HHP) treatment as a function of the treatment medium pH and composition and (ii) the relationship between the occurrence of sublethal injury and the inactivating effect of a combination of HHP and two antimicrobial compounds, tert-butyl hydroquinone (TBHQ) and citral. The three microorganisms showed a high proportion of sublethally injured cells (up to 99.99% of the surviving population) after HHP. In E. coli and L. monocytogenes, the extent of inactivation and sublethal injury depended on the pH and the composition of the treatment medium, whereas in S. cerevisiae, inactivation and sublethal injury were independent of medium pH or composition under the conditions tested. TBHQ alone was not lethal to E. coli or L. monocytogenes but acted synergistically with HHP and 24-h refrigeration, resulting in a viability decrease of >5 log(10) cycles of both organisms. The antimicrobial effect of citral depended on the microorganism and the treatment medium pH. Acting alone for 24 h under refrigeration, 1,000 ppm of citral caused a reduction of 5 log(10) cycles of E. coli at pH 7.0 and almost 3 log(10) cycles of L. monocytogenes at pH 4.0. The combination of citral and HHP also showed a synergistic effect. Our results have confirmed that the detection of sublethal injury after HHP may contribute to the identification of those treatment conditions under which HHP may act synergistically with other preserving processes.
authors.affiliation: Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Miguel Servet 177, 50013 Zaragoza, Spain.
authors.forename: Maria
authors.initials: M
authors.lastname: Somolinos
authors.forename: Diego
authors.initials: D
authors.lastname: García
authors.forename: Rafael
authors.initials: R
authors.lastname: Pagán
authors.forename: Bernard
authors.initials: B
authors.lastname: Mackey
mesh_terms: D000080462:Acyclic Monoterpenes; D000890:Anti-Infective Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry; D004357:Drug Synergism; D004926:Escherichia coli / Q000187:drug effects* / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D006873:Hydroquinones / Q000494:pharmacology*; D006874:Hydrostatic Pressure; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000502:physiology; D050296:Microbial Viability; D039821:Monoterpenes / Q000494:pharmacology*; D012034:Refrigeration; D012441:Saccharomyces cerevisiae / Q000187:drug effects* / Q000502:physiology
chemical_list: D000080462:Acyclic Monoterpenes; D000890:Anti-Infective Agents; D003470:Culture Media; D006873:Hydroquinones; D039821:Monoterpenes; C018855:2-tert-butylhydroquinone; C007076:citral